Advanced Materials Research Vol. 412

Abstract: The effects of low-temperature frit Li₂O-Na₂O-K₂O-B₂O₃-SiO₂-CaO-BaO-ZnO (abbreviated as BS) on the sintering behavior and electrical properties of 0.95K_0.49Na_0.51NbO₃- 0.05LiSbO₃ (abbreviated as KNN-LS) lead-free piezoceramics were investigated. The sintering temperature of the KNN-LS ceramics can be reduced from 1080 °C to 1000 °C due to the addition of BS frit. For the 0.5 wt% BS-doped KNN-LS ceramics, which are sintered at reduced temperature of 1000 °C for 2 h, remain relatively high piezoelectric constant d₃₃ (195 pC/N) and planar electromechanical coupling coefficient k_p (40.7%). In addition to other optimization effects, such as reduction of dielectric loss from 3.6% to 2.7% and increment of mechanical quality factor Q_m from 48 to 70, this BS frit was experimentally proved to be good for low temperature sintering of KNN-based ceramics while maintaining high piezoelectric response.

Abstract: Eu₂O₃-doped bismuth titanate (Bi_4-xEu_xTi₃O₁₂: BET) thin films with random oriention were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BET films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. The remanent polarization ( P_r ) and coercive field (E_c) of the BET Film with x=0.8 were 20μC/cm² and 65KV/cm , respectively. After 3×10¹⁰ switching cycles, 15% degradation of P_r is observed in the film.

Abstract: The electrical properties of Ce-doped bismuth titanate, Bi_4-xCe_xTi₃O₁₂ (BCT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.4 and 1.0 the current-voltage characteristics exhibited negative differential resistance behaviors and their P-E hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.6 and 0.8 the current-voltage characteristics showed simple ohmic behaviors and their P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( P_r ) and coercive field (E_c) of the BCT ceramic with x=0.8 were above 20μC/cm² and 60KV/cm , respectively.

Abstract: The electrical properties of La-doped bismuth titanate, Bi_4-xLa_xTi₃O₁₂ (BLT) ceramics prepared by a conventional electroceramic technique have been investigated. XRD analyses revealed Bi-layered perovskite structure in all samples, and indicted that Bi ions were only substituted near the Ti-O octahedron layers by La ions. SEM micrographs show randomly oriented and plate-like morphology. The remanent polarization ( P_r ) and coercive field ( E_c ) of the BLT ceramic with x=0.75 were above 19μC/cm² and 60KV/cm, respectively. The large value of remanent polarization and low coercive field of La-doped bismuth titanate ceramics promote these materials to potential applications.

Abstract: The ferroelectricity of Bi_3.25Dy_0.75Ti₃O₁₂ (BDT), and Bi_3.25Dy_0.75Ti_2.97V_0.03O₁₂ (BDTV) ceramics prepared at 1100°C by a conventional ceramic technique was investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (P_r) and coercive field (E_c) of the BDT ceramics are 15 µC/cm² and 64kV/cm, respectively. Furthermore, V substitution improves the P_r value of the BDT ceramics up to 23 μC/cm², which is much larger than that of the BDT ceramics. Therefore, co-sustitution of D and V in Bi₄Ti₃O₁₂ (BIT) ceramic is effective for the improvement of its ferroelectricity.

Abstract: Bi_3.25La_0.75Ti_2.97V_0.03O₁₂ (BLTV) ceramic were prepared by solid state reaction. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed plate-like grains with random orientation. BLTV caused a large shift of the Curie temperature ( T_C ) of Bi₄Ti₃O₁₂ (BIT) from 675°C to 395°C. The remanent polarization and the coercive field of the BLTV were 31μC/cm² and 54kV/cm at an electric field of 90kV/cm, respectively. Furthermore, the dielectric permittivity and dissipation factor were 300 and 3×10^-3 at 1MHz, at 1V and at room temperature, respectively. These ferroelectric properties of BLTV are superior to V-doped Bi₄Ti₃O₁₂ (~20μC/cm² and 80kV/cm) and (Sr, Ta)-doped Bi₄Ti₃O₁₂ (~12μC/cm² and 71kV/cm) ceramics. In addition, the dense ceramics of BLTV could be obtained by sintering at temperatures 100─200°C lower than those of the SrBi₂Ta₂O₉ system.

Abstract: The electrical properties of Gd-doped bismuth titanates Bi_4-xGd_xTi₃O₁₂) prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of Gd-doped sample exhibits a negative differential resistance behavior. The conducting filamentary model has been used to explain the negative differential resistance phenomenon in Gd-doped bismuth titanates. The impedance spectrum of Gd sample indicates that both consist of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi₄Ti₃O₁₂ and the distribution of every element is uniform. Gd-doped sample exhibites randomly oriented and plate-like morphology.

Abstract: La-doped bismuth titanate (Bi_4-xLa_xTi₃O₁₂: BLT) and pure Bi₄Ti₃O₁₂ (BIT) thin films with random orientation were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. La-doping into BIT caused a large shift of the Curie temperature ( T_C ) from 675°C to lower temperature and a improvement in dielectric property. The experimental results indicated that La doping into BIT also result in a remarkable improvement in ferroelectric property. The P_r and the E_c values of the BLT film with x=0.75 were 20 μC/cm² and 82kV/cm, respectively.

Abstract: The electrical properties of Dy-bismuth titanate (Bi_4-xDy_xTi₃O₁₂) prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of Dy-doped sample exhibits a simple ohmic behavior. The impedance spectrum of Dy-doped sample indicates that consist of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi₄Ti₃O₁₂ and the distribution of every element is uniform. Dy-doped sample exhibit randomly oriented and plate-like morphology.

Abstract: (n+n) structure semiconductor gas sensor based on the compensation-feedback principle is composed of two sensitive materials A and B which are all n-type materials. The results analyzed from a theoretical viewpoint show that the (n+n) combined structure semiconductor gas sensor has higher selectivity, better thermal stability and higher sensitivity than conventional sensors when the materials A and B satisfied certain conditions. Though testing the characteristics of the (n+n) combined structure semiconductor gas sensor, the perfect (n+n) combined structure acetone gas sensor is fabricated, and could be applied to monitor and control leakage of acetone gas.